In the nuclear power industry, radioactive contamination can generally be found (1) in solutions and (2) on surfaces. Aqueous treatment processes are used for high concentrations of radioactive contaminants in solution. Chemical decontamination technique have been used to decontaminate stainless steel components, other iron-based steel and alloys, metal surfaces, structural materials and equipment (e.g., glovebox, radioactive cells, process apparatus). Standard chemical dissolution can be achieved by injecting, circulating, and draining the chemical components (e.g., values and tools). Decontamination of nuclear facilities is necessary to reduce radiation field during normal operations and decommissioning of complex equipment. The complexity of equipment and location of radioactive contaminants in hard to reach places makes conventional aqueous processes cumbersome. Customary gel and/or foam decontamination processes are used to decontaminate hard to treat structures, however, neither gels or foams have shown the selectivity toward the decontamination of radioactive components for extensive commercial applications. Furthermore, the final disposal of the foams and gels are also awkward, and in this patent we demonstrate a new process that addresses the above mentioned issues.
A variety of chemicals are used to decontaminate surfaces including organic acid, complexants, and mineral acids see for instance Nunez et al. U.S. Pat. No. 6,504,077 issued January 2003, Horwitz et al. U.S. Pat. No. 5,078,894 issued January 1992, U.S. Pat. No. 5,332,531 issued Jul. 26, 1994, U.S. Pat. No. 5,587,142 issued December 1996 and the disclosures that are incorporated herein by reference. The Waller et al U.S. Pat. No. 4,810,405 issued March 1989 is also incorporated by reference. Strong acids will dissolve oxide scale; however, they will also dissolve the metallic substrate and have limited solubility in gel or foam systems. Weak acids such as organic acids (e.g., citric acid, oxalic acid, EDTA) are also added into decontamination solvents with the purpose of dissolving and complexing the dissolved metal oxide components. Additionally, the formation of gels and foams with the weak organic acids has shown negligible decontamination of surfaces. Various reviews have evaluated the need of Decontamination & Decommissioning (D&D) of surfaces and equipment within Department of Energy (DOE) and surveyed D&D processes suitable to DOE and industrial applications. In general, decontamination of equipment prior to decommissioning does not require the protection of the base metal. However, gel and foam processing can led to more efficient processing and reduce waste generation. In the current invention we discuss gel and foam based HEDPA chemical solutions which are unique in that they can provide protection to the base metal for continued application of the equipment and reduce the final waste form production to one step. The HEDPA based gels and foams can even be applied at room temperature which has not been effective in radioactive decontamination processes. Gel and foam based HEDPA processes allow for decontamination of difficult to reach surfaces unmanageable with traditional aqueous process methods. Also, the gel and foam components are optimized to maximize the dissolution rate and assist in the chemical transformation of the gel or foam to a stable waste form.
Radioactive decontamination techniques of stainless steel components, other iron-based steels and alloys, metal surfaces, and other structural materials e.g., concrete, tools, etc. have been unsatisfactory for many applications due to ineffective scale removal, target specificity (i.e. damage to the metal substrate), or waste handling problems. Chemical decontamination is achieved by the use of solvents to dissolve contaminated films or scale from the steel or metal substrates. Oxide scales are formed on stainless steels, iron-based alloys, and other non-ferrous surfaces in water systems at low and high temperatures and pressures. The dissolution of oxide scales can be achieved by injecting, circulating, and draining the chemical solvents from large equipment e.g. tanks, interior surfaces of pipes, coolant pipes and steam generators, and other facility components e.g., valves, tools. Decontamination of nuclear facilities is necessary to reduce radiation fields during daily operation, to facilitate eventual equipment handling and repairs, and for decommissioning and release of equipment and reuse of components. Currently, there are many available chemical techniques that can dissolve scales or films formed on ferrous metals, each with associated limitations. In order to develop more efficient chemical decontamination solvents, it is important to understand the formation of oxide scales. For boiling water reactors (BWRs) and pressurized water reactors (PWRs) there is a good chemical understanding of oxide scale and/or film formation.